Path-Q Solar
How much battery power is needed to run an electric heat pump during an outage?
Answer
Battery power must cover the heat pump's running demand and any startup or auxiliary-heating demand, while battery energy capacity must cover how long it will operate. The required size cannot be determined from the heat pump's nominal tonnage alone.
Key points
- Separate power in kilowatts, which determines whether the system can start and run the equipment, from energy in kilowatt-hours, which determines runtime.
- Check compressor startup characteristics and whether the system has electric resistance backup heat; resistance heat can require substantially more power.
- Outdoor temperature, building insulation, thermostat settings, cycling, and other backed-up loads change runtime.
- A load-management strategy may allow the heat pump to operate without backing up every household circuit.
What it depends on
- Heat pump nameplate running and startup requirements
- Auxiliary or emergency heat configuration
- Expected outdoor conditions and runtime
- Other loads sharing the backup system
Risks and trade-offs
- A battery may run the compressor but not high-demand auxiliary heat.
- Sizing for rare worst-case conditions can be expensive, while undersizing can cause shutdowns during an outage.
- Long outages may require load prioritization, reduced heating, or another energy source.
Information you may need
- Heat pump and auxiliary-heat nameplate data
- Desired indoor temperature and outage duration
- Critical-load list and measured household demand
- Battery inverter surge rating and usable capacity
Your next step
What to do next
Have a qualified designer perform a startup and runtime load calculation with auxiliary heat separately identified, then quote the required battery power and usable energy.
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SQ00569